Compounds that are weak acids are often poorly soluble at low (e.g., less than about pH 4 or pH 5) and at medium pH values (e.g., pH values of about 6 or 7). Such compounds are often difficult to use as pharmaceuticals due to, for example, poor solubility in pharmaceutically acceptable solutions. Thus, despite possible theoretical therapeutic efficacy, some compounds are not useful in clinical practice, or not as useful as they might be if methods and compositions were available to provide such compounds in pharmaceutically acceptable forms. In addition, formulations of such compounds may be unstable, and may be difficult to store for use, even if it were possible to prepare pharmaceutically acceptable formulations of such compounds.
Sulphonylureas and other compounds that act on sulphonylurea receptors (SURs) are useful in medical treatment of diabetes and other disorders. SURs may be of different types, including, for example, sulphonylurea receptor type 1 (SUR1) and sulphonylurea receptor type 2 (SUR2). Compounds that act at SURs include sulphonylureas (such as glibenclamide) and other compounds (e.g., repaglinide and taglizide). Sulphonylureas and other compounds active at SURs include glibenclamide (also known as glyburide), 4-trans-hydroxy-glibenclamide, 3-cis-hydroxy-glibenclamide, tolbutamide, repaglinide, nateglinide, meglitinide, midaglizole, LY397364, LY389382, glyclazide, glimepiride and other drugs or metabolites of drugs which interact with SURs.
In addition, ion channels such as potassium channels and non-selective channels may be associated with SURs (e.g., a NCCa-ATP channel; see, for example, U.S. Pat. No. 7,285,574, hereby incorporated by reference in its entirety, or an ATP-sensitive potassium channel (KATP channel)). Compounds active towards ion channels associated with SURs are also useful in medical treatments. Some compounds that act on non-selective channels that may be associated with SURs include, for example, pinkolant, flufenamic acid, mefanamic acid, niflumic acid, rimonabant, and SKF 9635. In addition, other compounds may act on or affect the action of SURs and/or ion channels associated with SURS, including, without limitation, for example, steroids and steroid derivatives and related compounds such as estrogen, estradiol, estrone, estriol, genistein, diethystilbestrol, coumestrol, zearalenone, non-steroidal estrogens, and phytoestrogens.
Glibenclamide Solubility
Glibenclamide solubility in various solutions has been reported, and is typically reported as being very poorly soluble in buffered aqueous solutions. For example, the solubility of glibenclamide in buffered aqueous solutions has been reported by Glomme et al. (Glomme A, Marz J, Dressman J B. Comparison of a miniaturized shake-flask solubility method with automated potentiometric acid/base titrations and calculated solubilities. J Pharm Sci. 2005 January; 94(1):1-16). The buffered aqueous solution was made with distilled water to form a potassium chloride (220 mM) solution buffered with potassium phosphate (29 mM), and the pH adjusted to pH 5, 6, or 7 with sodium hydroxide. These solutions had osmolarities of between about 280 to 310 milliOsmolar and had buffer capacities of about 10±2 milliEquvialents/L/pH. Glomme et al. report that glibenclamide is only sparingly soluble in such solutions, with extremely low solubilities at pH 2, 3, 5, 6, and 7, and relatively greater (although still very low) solubilities at pH 8, 9 and 11.8. These solubilities are shown in TABLE 1:
TABLE 1Solubility of Glibenclamide at 37° C. (aqueous).pHSolubility (mg/mL)20.0000730.0000650.000160.0006270.0056280.051290.098611.80.5316
It can be seen that glibenclamide in such aqueous solutions is poorly soluble, that the solubility is less at acidic pH, and that the solubility increases by an order of magnitude from pH 6 to pH 7, from pH 7 to pH 8, and from pH 8 to pH 11.8.
Similarly, low glibenclamide solubilities in aqueous solutions were reported by Kaiser et al. (Kaiser D G, Forist, A A. A review of Glibenclamide Metabolism in Man and Laboratory Animals. Physical and Analytical Chemistry Research, The Upjohn Company; 1975), with solubilities of below 1 mg/mL at all measured pH values from pH 4 to pH 9. Glibenclamide was dissolved in Britton-Robinson buffer. (Britton-Robinson buffer is an aqueous buffer solution including phosphoric acid, acetic acid and boric acid, with the pH adjusted with sodium hydroxide.) These solubilities are reported in TABLE 2.
TABLE 2Solubility of Glibenclamide at 27° C. (aqueous).pHsolubility (mg/mL)40.00460.00570.01180.08090.600
Rydberg et al. (Rydberg T, Jonsson A, Roder M, Melander A. Hypoglycemic activity of glibenclamide (Glibenclamide) metabolites in humans. Diabetes Care. 1994 September; 17(9):1026-30) also reported a glibenclamide solubility of 0.5 mg/mL in a 0.1 M, pH 10 phosphate-buffered aqueous solution (300 mOsm/L).
The following formulation for intravenous glibenclamide (1 mg/mL) was developed for a Mayo study (Schrage W G, Dietz N M, Joyner M J. Effects of combined inhibition of ATP-sensitive potassium channels, nitric oxide, and prostaglandins on hyperemia during moderate exercise. J Appl Physiol. 2006 May; 100(5):1506-12. Epub 2006 Feb. 9):
IngredientAmountGlibenclamide500 mgSodium Chloride 0.9%450 mL0.1 N Sodium Hydroxide50 mLAbove formula makes500 mLType of container5 mL amber vialAmount in each5 mLShelf lifeUnknown
The formulation can be prepared by: i) mixing sodium hydroxide and sodium chloride in water; ii) dissolving glibenclamide in the mixture, with slight warming to help dissolve it; iii) filter the solution through a 0.22 micron filter into sterile 5 mL amber vials; iv) stopper, cap and crimp. Sterility can be tested by using a Millipore system, and while working in the laminar flow hood: i) pass the test solution through the filter and flush with sterile saline injection three times; ii) crimp the hoses and inject the culture media into the container; iii) record the product information on form #11.31, and staple to the compounding formula; iv) perform a LAL test using a 1:20 dilution; v) quarantine for 14 days and check daily for presence or absence of growth; vi) record all culture results on the culture report form and the Microbial Culture Journal.
Betageri et al. (Betageri, G. V. et al. Enhancement of dissolution of glibenclamide by solid dispersion and lyophilization techniques, Int. J. Pharm. 126, 155-160 (1995)) evaluated increasing solubility of glibenclamide first by addition of various polyethylene glycol (PEG) and then via various PEG forms plus lyophilization. Betageri did not lyophilize glibenclamide on its own, and the procedures were performed at pH 7.4 in buffered solutions. Glibenclamide-PEG was found to be more soluble than glibenclamide alone. It is to be noted that all the Betageri formulations involve one or more PEG, and that the concentrations are very low.
Lyophilization
Lyophilization is a term used to describe methods and actions that provide dried materials, such as powders, from liquids containing solids or dissolved materials by freeze-drying (freezing a liquid containing dissolved or suspended material, and drying while frozen by sublimation) to provide a dry solid containing the dissolved or suspended material in solid form. Typically, aqueous solutions are used in lyophilization, although mixed aqueous/solvent solutions, and other liquid solutions, may be used. For example, a biological material may be lyophilized from a solution or suspension in which it is mixed with protective agents. Such a solution or suspension may then be frozen, and subsequently dehydrated by sublimation. Sublimation may optionally be followed by further drying steps.
Many materials and chemicals may be lyophilized. For example, dilute chemicals, including organic molecules such as drugs, hormones, proteins, nucleic acids (e.g., DNA and RNA), lipids, and carbohydrates or other molecules, may be lyophilized to provide a dried form of a chemical or mixture of chemicals. Biological samples may also be lyophilized. Typically, lyophilization methods include freeze-drying a liquid solution or suspension to provide a dry residue containing a high concentration of the dissolved or suspended compounds. In some cases, the solid provided by lyophilization may be or include a salt.
Lyophilization processes provide solids, such as powders, dried films, or cakes. Small particles may be obtained, if desired, from such powders, films, or cakes by procedures such as grinding or flaking.
However, some methods of lyophilization may be improved.
In addition, some materials may be difficult to lyophilize. Some materials, including some organic molecules useful in pharmaceutical applications and as medicaments, are difficult to dissolve or suspend in a solution, particularly in aqueous solutions of neutral or near-neutral pH, or in buffered aqueous solutions.
Thus, the need exists for improved methods of lyophilizing materials suitable for a wider range of materials than is presently available, and for particular desired materials and for desired types of materials.